It is conventional practice, for the metallurgical treatment of a molten metal, to supply the vessel provided for the treatment operation with additive substances, in addition to the charge material (ores or metals in a solid or liquid condition) in order to accelerate slag formation and to provide the desired composition for the molten metal bath. The additive substances are added to the molten metal either together with the charge material when the vessel is being charged or during the melting process or at the beginning of the refining phase.
British patent specification No 843 714 describes a method of prolonging the service life of the refractory lining of a Kaldo converter. That publication states that, when oxygen is blown on to the molten iron during the refining procedure, it is generally not sufficient to supply the molten bath with coolant such as limestone, quicklime or iron ore in order to resist excessively high temperatures. It is stated that, at the average temperature of the molten metal, which is required for carrying out the process, local overheating occurs in the region of the converter in which the jet of oxygen encounters the molten metal and reacts therewith. Due to radiant heat from that area and post-combustion of the carbon monoxide which issues, local overheating and damage to the lining of the converter is then caused. In order to prevent that from happening, at least a part of the required coolant is blown through a lance in the granular condition by means of a carrier gas such as water vapour or carbon dioxide, against the region of the refractory lining which is subjected to the highest thermal loading. That procedure provides an effective screening action. At the same time the lime which remains clinging to the wall protects the latter from chemical attack by the slag and insulates it to prevent the transmission of heat. In that way it is possible substantially to increase the service life of the refractory lining of the furnace. The grain size of the lime is said to be in the range of from 0.5 to 10 mm and the amount of lime required is specified as being about 130 Kg/t to 140 kg/t of crude iron.
German patent specification No 2 210 713 discloses a process for protecting the refractory walls of a converter during operation thereof, wherein carbon-bearing material is continuously or periodically applied to the inside wall surface, as a wearing material. That is effected by introducing a carbon-bearing material in a pasty form or in a form of being capable of flow, by way of wall nozzles distributed in the converter around the periphery thereof. Thus for example hot oil or tar or pitch is introduced through wall nozzles disposed above and below the surface of the bath, during the metallurgical treatment of the molten iron.